The present invention relates to implantable medical devices (IMDs), and in particular to devices for automatically determining and monitoring an ischemia threshold in patients suffering from coronary artery disease.
Ischemia occurs when the myocardial demand for oxygen exceeds the delivery capacity of the cardiac circulation. Coronary artery disease (CAD) is the largest cardiovascular comorbidity in patients with implanted pacemakers and defibrillators. The most common symptom of patients with CAD is stable angina, an episode of myocardial ischemia accompanied with symptoms. One hallmark of stable angina is the reproducibility of the symptoms at specific workloads.
Many implantable pacemakers and cardioverter/defibrillators feature rate-responsive pacing, in which the pacing rate is adjusted upward as a function of sensed activity (either alone or in conjunction with sensed respiration). For patients having CAD, rate-adaptive pacing can result in a pacing rate that exceeds the ability of the patient's heart to supply sufficient blood flow to the myocardium. As a result, a CAD patient can be paced beyond a patient's ischemic threshold.
Devices have been proposed that sense ischemia, and reduce the pacing rate when ischemia is detected. Examples of devices including ischemia detectors include Ekwall U.S. Pat. No. 6,256,538, Ekwall, et al. U.S. Pat. No. 6,264,606, Lu U.S. Pat. No. 6,604,000, Kroll U.S. Pat. No. 6,865,420, Zhu Publication No. US 2003/0060854, Stahmann, et al. Publication No. US 2004/0133247 and Yu, et al. Publication No. US 2005/0137631.